Pregnane X Receptor (PXR) Increases Urine Concentration by Upregulating Hypothalamic Arginine Vasopressin Expression

Background: PXR, a ligand-activated nuclear receptor superfamily transcription factor, is constitutively expressed in the hypothalamus and kidney. Body water homeostasis is essential for human health. The most crucial and well-established regulatory mechanism for maintaining body water homeostasis is the hypothalamic-kidney axis, which precisely controls renal urinary excretion to maintain plasma osmolarity within a tightly regulated physiological range. Increasing evidence suggests that there are many other factors involved in the regulation of water homeostasis in addition to the AVP-V2R-AQP2 pathway. LXRβ promotes urine concentration by increasing the expression of central AVP and renal AQP1. FXR promotes urine concentration by upregulating renal AQP2 transcription. However, the role of PXR in water and salt metabolism remains largely unknown. Methods: We treated C57BL/6 mice with pregnenolone 16α-carbonitrile (PCN), a rodent PXR agonist, and constructed global PXR knockout (PXR-/-) mice by deleting exon 3 to determine urine output changes through volume collection and osmolality measurements. Hypothalamic AVP expression was analyzed by qPCR and western blotting. PXR directly targets the AVP gene as evidenced by luciferase-ChIP-EMSA assays. Results: We found that treatment with PCN, significantly reduced urine volume and increased urine osmolarity in mice. In contrast, PXR−/− mice exhibited impaired urine-concentrating ability, leading to a polyuria phenotype. Additionally, treatment of mice with PCN significantly upregulated, while PXR gene deficiency substantially reduced, AVP expression in the hypothalamus. In addition, PXR activation by PCN or adenovirus-mediated PXR knockdown had little effect on the mRNA and protein levels of AQP2 and AVP in cultured inner medullary collecting duct cell line (mIMCD3). Bioinformatic analysis showed that the mouse AVP gene promoter contains a putative PXR response element (PXRE). The luciferase reporter, ChIP and EMSA assays further revealed that PXR can bind to the PXRE, resulting in a significant increase in AVP gene transcription. Conclusion: Activation of PXR can increase urine concentration, while deficiency of the PXR gene impairs urine concentration capacity. PXR is co-localized with AVP in the hypothalamus where it upregulates the transcription of its target gene AVP, thereby enhancing renal water reabsorption.